Huygens explained repetition pitch by equating echo spacing with musical interval timing in 1693

Evidence

When one is standing between the staircase and the fountain, one hears from the side of the staircase a resonance that possesses a certain musical pitch that continues, as long as the fountain spouts. One did not know where this tone originated from or improbable explanations were given, which stimulated me to search for a better one. Soon I found that it originated from the reflection of the noise from the fountain against the steps of the staircase. Because like every sound, or rather noise, reiterated in equal small intervals produces a musical tone, and like the length of an organ pipe determines its own pitch by its length because the air pulsations arrive regularly within small time intervals used by the undulations to do the length of the pipe twice in case it is closed at the end, so I imagined that each, even the smallest, noise coming from the fountain, being reflected against the steps of the staircase, must arrive at the ear from each step as much later as the step is remote, and this by time differences just equal to those used by the undulations to travel to and fro the width of one step. Having measured that width equal to 17 inches, I made a roll of paper that had this length, and I found the same pitch that one heard at the foot of the staircase. — Eric J. Heller, Why You Hear What You Hear- An…, 2139

Categorization

• CANDY: Huygens verified his pitch theory by rolling up paper to the measured stair width and listening — wonderfully hands-on 17th-century science.